The present invention relates to a binding wire twisting and tightening mechanism in a reinforcement binding machine which, after a binding wire is sent out in a loop shape and is wound around reinforcements, twists part of the binding wire to thereby tighten the same.
Generally, when placing a reinforced concrete on a building or a structure, a concrete is placed after reinforcements arranged so as to intersect each other vertically and horizontally are bound together and, recently, an operation to bind the reinforcements together has been carried out by a reinforcement binding machine. As an example of such reinforcement binding machine, there is known a reinforcement binding machine, in which, as shown in Japanese Utility Model Application Laid-open No. Hei. 5-3494 filed by the present applicants, a wire is wound around reinforcements in a loop shape and, after then, the looped portion of the wire is in part gripped and rotated by a pair of twisting hooks to thereby twist and tighten the wire so that the reinforcements can be fixed.
The above-mentioned hooks are normally situated in the rear of the looped portion of the wire and, after the wire is wound around the reinforcements, the hooks can grip the wire to twist and tighten the same. In this case, there is necessary a pulling operation that, after the reinforcement binding machine is pulled toward an operator to thereby cause the looped portion of the wire to be tensed, the wire is closely contacted with the intersecting portions of the reinforcements before the wire is twisted.
Also, by pulling the reinforcement binding machine toward the operator, a tensile force is given to the looped portion of the wire, which in turn causes the winding and tightening force of the wire to increase. However, as shown in FIG. 23, the twisted portion 121 of the wire 120 is caused to rise up long in a direction perpendicular to the surfaces of the reinforcements a and, therefore, if the concrete is placed while the wire twisted portion 121 remains as it is, then the wire twisted portion 121 is exposed out from the surface of the concrete. This requires a troublesome operation to bend the wire twisted portion 121 in such a manner as shown by an arrow 122 after twisted, while the bending of the wire twisted portion 121 loosens the tension of the wire 120 to thereby lower the reinforcements binding force of the wire 120.
In view of the above, as disclosed in Japanese Patent Application No. Hei. 7-79896, there is provided a technique in which a wire is twisted and tightened while the distance between the twisted portion of the wire and the reinforcements is maintained at a given level. However, according to this technique, although the loop diameter of the wire can be reduced by twisting the wire, any special resistance or tensile force cannot be applied to the wire during the wire twisting operation. Also, the twisting hooks are structured such that their rotational movements can be stopped when they detect only the twisting torque in the wire twisted portion but cannot be stopped by the total winding and tightening force thereof. Therefore, according to the disclosed technique, the whole binding force obtained is unstable.
There is known another binding machine which is disclosed in Japanese Utility Model Application Laid-open No. Hei. 5-92103. In this reinforcement binding machine, after a binding wire is fed out and guided from a wire reel, around which the binding wire is wound, in such a manner that the wire can be wound in a loop shape around the peripheries of reinforcements to be bound together, the thus wound wire is cut off from the wire wound around the wire reel, and part of the wire wound in a loop shape is gripped and twisted, so that the reinforcements can be bound together. However, since the leading and trailing ends of the wire are free when the wire is twisted, they are easy to be swung in various directions with respect to the reinforcements binding portion of the wire. In view of this, the leading end of the wire can be adjusted according to the amount of feeding of the wire so that it comes near the reinforcements binding portion of the wire.
However, the terminal end of the wire is fixed to a cutting mechanism, and the position where the end of wire is fixed is far from a twisting mechanism. When the reinforcement binding machine is pulled apart from the binding wire, the terminal end 204a of the wire 204 binding the reinforcements 206 should be normally situated at such a position as shown by a dotted line in FIG. 24. Actually, due to the above-mentioned reasons, the wire terminal end 204a can be caught by part of the reinforcement binding machine or by part of the reinforcements so that the terminal end 204a can be swung beyond the covering thickness of the concrete 218. In this case, since the wire terminal end 204a is exposed externally of the concrete 218, there is a possibility that rain water can penetrate into the concrete through this and the exposed portion of the wire terminal end 204a can be oxidized to thereby cause a crack.
Not only that, in this reinforcement binding machine, as shown in FIG. 25, when the twisting hooks are rotated for twisting the wire 320, the wire 320 is swung right and left, with the result that the winding portion of the wire 320 can be shifted from the best position that is shortest in distance from the mutually intersecting portions of the reinforcements 321.
Since the wire twisting mechanism is caused to stop when the twisting torque of the wire reaches a given value, the swinging of the wire can also be corrected. However, since the reinforcements 321 respectively include ribs 322, when the wire 320 is in engagement with the ribs 322, the wire 320 is swung in such a manner as shown in FIG. 25 and is thereby bound in such a manner that it is extended longer than expected. In this case, when the concrete is placed, the engagement between the wire and ribs can be removed to thereby unstabilize the bound condition of the reinforcements.